Vehicle Range Limitations Involved in Use of Alcohol Fuels in FFVs
Although there can be environmental and other benefits for vehicle use of high blend alcohol fuels (such as E85), consumer acceptance remains a barrier to widespread use of the fuel, particularly in the United States. One commonly stated factor holding back widespread consumer demand of E85 is the lack of vehicle range per tank of fuel when comparing E85 with traditional gasoline blends (e.g. E0\E10). This factor is a two-fold consequence of the lower energy density of pump grade E85 as compared to E0 (about 80% of the energy per gallon) and a typically lower engine brake efficiency in running on E85 in a flex fuel vehicle (FFV). The combination of these two effects results in a reduction in vehicle range of 20%-30% for a typical flex fuel vehicle operating on E85. With this disparity, E85 in the U.S. generally offers a financial disincentive in terms of fuel cost per mile traveled.
Thus, there exists a need for a flex fuel vehicle that offers similar miles traveled per gallon of fuel for both regular gasoline and E85 (or at least close enough to commercially justify for the consumer more widespread use of E85 fuel).
Difficulties in Treating Emissions in Lean Burn Engine Systems
It is known in the art that lean combustion of gasoline and other fuels can increase the efficiency of an internal combustion engine system by 15% or more. As a result of these efficiency improvements, lean combustion gasoline engines have found commercial success in many parts of the world. Combined cycle engines, which operate lean at low loads, and at stoichiometry at higher loads, are also known (see, e.g., commonly assigned U.S. Pat. No. 5,549,087 to Gray and Hellman). However, gasoline engines that operate lean have not been commercialized in the United States due to difficulties in meeting U.S. emission requirements. In particular, lean combustion is not compatible with conventional three-way catalysts typically used for gasoline engines. In addition, other aftertreatment technologies that may be used with lean combustion engines are subject to sulfur poisoning. For example, the sulfur tolerance limit of SCR and LNT/LNC (i.e. Lean NOx trap/Lean NOx catalyst) systems are approximately 15 ppm to 25 ppm. In contrast, sulfur levels in U.S. gasoline are typically around 30 ppm, but can range up to 80 ppm, thus requiring an aftertreatment system that can tolerate a high proportion of usage of 80 ppm sulfur without deactivating or degrading the aftertreatment system.